One of the core concepts in Ayurveda is the recognition of seven fundamental substances, called the Seven Dhatus or Saptadhatu, which support the basic structure and functioning of the body, both for physical and psychological health.
These Dhatus are associated with lymph or plasma (rasa), blood (rakta), muscles (mamsa), fat (medha), bones (ashti), bone marrow and nerves (majja) and reproductive fluid (shukra), the latter being sperm and ovum.
The Dhatus respond to the state of the Doshas. When the Doshas are out of balance they affect the Dhatus, which can become either deficient or excessive. Subsequently, illness can occur.